I have mentioned these here before, but watching them really conveys the brilliance of the creators. Watching any of these is indistinguishable from an actual TOS episode, but it has all new actors, and EXACT replicas of every set seen in TOS. Down to every detail, including the actual colors used in TOS for walls, sets, lights, etc. Paramount allows these to be made, under a limited license. Check this one out, called Lolani (full episode). CBS may step in at some point in the future, but it is not likely.
There are others at Star Trek Phase II. But this one comes from here: http://www.startrekcontinues.com/
There are others at Star Trek Phase II. But this one comes from here: http://www.startrekcontinues.com/